The knowledge of the currents in deep waters is important in the oil well drilling techniques out at sea, especially for calculating the stresses on the immersed structures. Further, if action by divers or submarines is required, it is important to know the speeds of the currents for safe working. Another application is the search for nodules.
It is known to measure the speed and the direction of the currents by means of a propeller current meter fixed to the sea-bed by means of an anchoring line.
The drawbacks of this device are that it only provides a pinpoint measurement, limited in accuracy because of the friction of the propeller and limited in depth because of the difficulty of providing too long an anchoring line.
It is known furthermore to measure the currents by means of a Doppler effect sonar. The signals used are obtained by volume reverberation of the acoustic waves. These devices supply the speeds of the currents in different depth ranges with good accuracy but have the drawback of not being able to be used in depths exceeding 1000 m because of the absorption of the acoutic waves and the divergence of the beam emitted by the sonar.
The device of the invention remedies these drawbacks by allowing currents to be measured in real time on board a boat for depths able to exceed 6000 m with slices of depth measurement of a thickness between 5 and 40 m and with an accuracy for the speed of the currents reaching 0.15 m/sec.